The use of free running transistor or field effect transistor-oscillators in, low, medium and high power inverters for generating a periodic output from a direct current power source is widespread. Indeed, it is also known in conjunction with free running inverters or converters to provide frequency synchronization which is capable of maintaining a constant frequency regardless of varying load and supply voltage; this has been done without altering the specific charcteristic of the saturable transformer which provides feedback.
In general in the past this has been achieved by using external drivers for the power transistors or field effect transistors of the inverter and this approach was capable of providing fixed frequency square-waveform inverters.
Such driver techniques are, however, not always advantageous and may have a variety of drawbacks including the need for highly complex drivers, the fact that the power transistors or field effect transistors do not always operate within their safety limits during the switching operations, protection against short circuit and overloads requires complex circuitry, and there is a risk of simultaneously switching the two power transistors or field effect transistors into an on state during switching.